NGWA develops checklist for hiring geothermal drilling contractors

July 5, 2011
WESTERVILLE, OHIO — Contractors, mechanical engineers and others involved in geothermal heat pump installations should evaluate qualifications of drilling contractors.

WESTERVILLE, OHIO — Contractors, mechanical engineers, architects, developers, and others involved in geothermal heat pump installations should evaluate the qualifications of drilling contractors to protect groundwater and optimize heat pump system operation, noted the National Ground Water Association, which has developed a list of pertinent questions professionals should ask drilling contractors.

The list can be accessed here at NGWA’s Website.

Estimates by the industry suggest that as much as 50% of the total geothermal heat pump market involves the use of vertical borehole subsystems. There are several different configurations of geothermal heat pump system installations involving vertical Earth drilling:

Open loop: Single well for water withdrawal, water returned to a surface source.

Open loop: Single well for water withdrawal, water returned to a second well.

Standing column: Single well for water withdrawal and water return.

Closed loop: Vertical boreholes.

Direct exchange (DX): Vertical boreholes using concentric pipe systems.

Experienced geothermal heat pump installers confirm that it is critical these systems 1) be installed with a properly constructed borehole, 2) equipped with a properly placed loop tube assembly, and 3) have properly grouted boreholes, not only for optimal heat transfer but also for groundwater protection.

To find drilling contractors, including those who work on geothermal heat pump installations, use the "Contractor Lookup" service on NGWA's web site.

Contractors should also check out NGWA's Guidelines for the Construction of Vertical Closed Loop Heat Pump Systems in the bookstore at

The lengthy checklist covers items such as licensing, certifications and accreditations. Is the drilling contactor a member of an association, such as NGWA or the International Ground Source Heat Pump Association?

Typical questions in the checklist include:

How many loop wells has this drilling firm drilled as this firm?

What drilling methods is the drilling contractor proficient in?

Can he produce an acceptable work history with a specific method?

Does this firm have experience drilling in the geology likely to be encountered at your job site?

Does the drilling firm have qualifications and experience to design the loop field?

Is the drilling firm being assigned this responsibility?

Does this firm have experience in mixing, pumping, and placing by pressure tremie method so-called thermally enhanced bentonite grout?

NGWA, a nonprofit organization composed of U.S. and international groundwater professionals — contractors, equipment manufacturers, suppliers, scientists, and engineers — is dedicated to advancing groundwater knowledge. NGWA’s vision is to be the leading groundwater association that advocates the responsible development, management, and use of water.

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